XPS 15 9550 - Slow with external display different scaling
When switching between laptop+external monitor to only laptop screen several times (when needing to leave the office desk for various reasons) things on the external monitor get quite slow. When using Chrome, for example, a new page will scroll noticeably slower, and will often flash maybe half of the screen as it's loading a new page. Even closing and opening Chrome again doesn't fix the issue. And it only happens when Chrome is displayed on the external monitor - on the laptop screen it seems to work fine.
I have the 9550, with 4K screen. My external monitor is 2560x1440 32", which means it scales at 100% whereas the 4K laptop screen goes to 250%. I know that many of the issues with scaling are Windows and not Dell, but I highly suspect a driver issue.
RE: XPS 15 9550 - Slow with external display different scaling
I have a very similar issue, except the flashing happens from start up. It seems to smooth out and stabilize after ~5-10 minutes. My setup is the XPS 9550 (bought in Nov. 2016) with 4k screen and a 27 inch QNIX QX2710 2560x1440 external monitor hooked up through the Thunderbolt 3 port with a Thunderbolt 3 to Dual-link DVI adapter.
The only thing that seems to work is to sign out of Windows and resign back in, once you connect the external monitor. This resets the scaling and text sizing effects and stabilizes the picture for me. Have you had any success figuring this out?